1. Field of the Invention
The present invention relates generally to a light emitting diode lens for a backlight and, more particularly, to a light emitting diode lens for a backlight, which radiates light, emitted from a light emitting diode light source, in lateral and vertical directions of a lens body, thus improving the uniformity of luminance and color in the overall system to which the LED lens is applied.
2. Description of the Related Art
Recently, in a display device and an illumination optical system, demands for a light source having environment-friendliness, high efficiency and a long lifespan are increasing. Furthermore, as the efficiency and luminance of a Light Emitting Diode (LED) are increasing continuously, an alternative light source using an LED has been developed and is gradually being applied to the display device and the illumination optical system. In particular, as projects, such as the development of an environment-friendly TeleVison (TV), are published, research into an LCD display device using an LED light source continues to advance. In order to meet such technical demands, the need for the development of a more efficient type of LED lens (or a lens for an LED light source) for a light source for the display device and the illumination optical system is further increasing.
FIG. 1 shows an example of a conventional side radiation-type LED lens, the details of which have been described in U.S. Pat. No. 6,679,621. The LED lens of FIG. 1, which is called a side radiation-type LED lens, is characterized in that it includes a reflecting surface and a refracting surface, and is configured such that light emitted from an LED is radiated through the side surface (refracting surface) of the lens.
The lens 20 of FIG. 1 is constructed to accommodate an LED 10 in the lower portion thereof, and includes a lower refracting surface 22, an upper refracting surface 24 connected to the lower refracting surface, and an upper reflecting surface 26. The upper reflecting surface 26 is symmetrical with respect to a central axis C and forms a predetermined angle, so that all of the light oriented in a vertical direction of the lens is reflected.
That is, as indicated by reference characters L1 and L2 in FIG. 1, the light emitted from the LED light source 10 is directly radiated in a lateral direction through the lower refracting surface 22. Furthermore, light oriented in the vertical direction is reflected in a Total Inner Reflection (TIR) fashion by the upper reflecting surface 26 and is then radiated in the lateral direction through the upper refracting surface 24.
However, although the LED lens having the above-described structure was designed with the goal of radiating all of the light in the lateral direction, there are light beams radiated through the upper surface of the lens, as indicated by reference characters L3 and L4 in FIG. 1. This phenomenon occurs because the lens has been designed under the condition that the LED light source accommodated in the lens is a point light source and, therefore, light, which is emitted from regions other than the focal point F of the LED light source, passes through the upper reflecting surface without being reflected therefrom. This light results in erroneous light in the lens. Such erroneous light degrades the performance of the overall system and the uniformity of color and luminance, therefore it may act as a factor that can increase the thickness of the overall system.
Furthermore, in the above-described side-emitting lens, most of the light beams are radiated in the lateral direction of the lens (that is, in the direction perpendicular to the display plane), so that a medium (for example, the internal reflecting plate of the backlight) for changing the path of light is required such that the light radiated in the lateral direction is directed toward the display plane. This can also degrade the overall performance of the light.
FIG. 2 shows another example of a conventional upper-emitting LED lens. In accordance with FIG. 2, the conventional upper-emitting LED lens is basically characterized in that LED light sources 32 are located at the center portion of a flat-shaped light guide plate 30, light emitted from the LED light source 32 is primarily reflected, is reflected again by a predetermined pattern 34 formed in the lower surface on the light guide plate, and is then radiated through the upper surface 36 (display surface) of the light guide plate 36.
That is, the upper-emitting LED lens of FIG. 2 is characterized in that the direction of the light, which is emitted from the LED light source, and the display direction are arranged parallel to each other, so that the light can be uniformly radiated.
However, although, in such a scheme, improvement in the efficiency of the overall system may be expected, there is a problem in which luminance variation among individual light sources causes non-uniformity of the overall system because the backlight system is not constructed using only a single light source. That is, in a system in which a single light source is used, the overall uniformity of the luminance thereof can be easily ensured. In contrast, in a system in which a plurality of LED light sources is arranged, a problem occurs in that the overall luminance is non-uniform because the light beams emitted from respective light sources overlap or have spacing intervals therebetween.